Tolls on the State Route 520 bridge begin this summer, but research from the University of Washington shows that those tolls may not unfairly burden low-income households.

When all low-income households in the Puget Sound region are considered, not just ones using the 520 bridge, a household earning $15,600 a year would pay an average of $10.50 or 0.07 percent of its annual income in tolls, compared with $63 or 0.08 percent for a household earning $76,350. This means that a toll on the bridge would be distributed roughly proportional to income across all households in the region.

State Road 520 crossing Lake Washington to the Eastside on the Evergreen Point Floating BridgeLucia Sanchez

“When examined this way,” said Robert Plotnick, a professor at the UW Evans School of Public Affairs who led the research, “tolling the 520 bridge does not create disproportionate burdens on low-income residents and is less burdensome than other ways of financing road construction such as gas or sales taxes, which would affect all low-income households and be regressive.”

However, low-income users of the 520 bridge will pay a greater percentage of their income than higher-income users. For example, the peak toll of $3.50 on the 520 bridge would mean that a household earning $15,600 annually (median for low-income households) would pay $1,680, or almost 11 percent of its income for tolls each year if its commute includes the 520 bridge during peak hours. That $1,680 would represent only 2.2 percent of income for a household earning $76,350 (median for non-low-income households).

Plotnick and his colleagues studied how tolls on heavily-used segments of the six major highways in the Puget Sound region (I-5, 405, I-90, State Road 520, State Road 167 and State Road 99) would affect both low-income and higher-income households. They found that tolls would cost low-income drivers a greater percentage of their income than higher-income ones. Low-income drivers would wind up spending almost four times more of their income than wealthier ones.

This would be a regressive situation in that the tolls would place a greater financial burden on poorer drivers than wealthier ones.

But the researchers also found that the extent of regressivity in tolling depends on whether the impacts are examined only across users of tolled roads or across all low-income households.

If toll costs were spread across all households in the Puget Sound region, not just the 1 percent of low-income households and 5 percent of higher-income ones who use the 520 bridge, the financial burden on low-income households would not be disproportionate.

The study resultsappear in the February issue of the Journal of Urban Affairs. Plotnick and his colleagues examined car ownership and transportation patterns among low-income and higher-income households. They used data from the Puget Sound metropolitan region and geographic information system methods to map driving routes back and forth to work.

To the researchers knowledge, its the first time geographic information systems methods have been used to map commuter routes in order to model tolling schemes. The study also provided insight on how equity effects differ within income groups as well as between them.

The Washington State Department of Transportation will begin tolls on the State Road 520 bridge this summer. Tolls will vary by time of day and range from $1.10 to $3.50 with Good To Go accounts. Tolls billed by mail are expected to cost an additional $1.50. From 11 p.m. to 5 a.m., travel on the bridge will be free.

The money will help pay for the new bridge, which crosses Lake Washington, connecting Seattle and Bellevue.

Besides Plotnick, authors of the paper are Jennifer Romich, an associate professor at the UW School of Social Work; Jennifer Thacker, a staff member at the nonprofit Burst for Prosperity; and Matthew Dunbar, a specialist in geographic information systems at the UW Center for Studies in Demography and Ecology.

The research was funded by the Washington State Department of Transportation.

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For more information, contact Plotnick at 206-685-2055 (o) or 206-930-5111 (cell) or Plotnick@uw.edu.